The field of the invention pertains to the injection molding of hollow plastic articles and, in particular, to preforms for bottles, syringes and other long slender hollow articles having one end closed and the other end open. The hollow interior is typically shaped by a core-pin. In processing the injection molding of parts that utilize a core-pin, such as medical syringes or bottle preforms, the core-pin forms the inner diameter of the part, and ideally maintains the part inner diameter concentric with the outer diameter. Unfortunately, the effectiveness of this pin is influenced by non-uniform fill and pack pressure, and nonuniform cooling gradients across the part wall. The non-uniform pressures and cooling gradients cause the core-pin to deflect off center and upon hardening (cooling) of the part, dimensional requirements of the wall thickness are not met.